The progress in the manufacturing process of a semiconductor and the trend in promoting circuit function of chips have fostered circumstances of providing highly condensed IC accompanied with enormously increased input/output connection points, resulting in problems in packaging an IC chip and further difficulties in integrating chips and printed circuit boards. Various schemes have been suggested to provide solutions to these problems and difficulties, among which flip chip package has broadly drawn attention.
A conventional flip chip package is shown in FIG. 1 in which bumps or solders are formed, on the surface of one side of chip 10, as connection points 12, and corresponding bonding pad is formed on the surface of printed circuit board 14 for being welded with connection points 12.
There are many drawbacks with the above flip chip package, among which one is the indispensable requirement of higher accuracy in forming connection point 12 to avoid short circuiting or breaking in the process next to (or after) the formation of connection point 12. The short circuiting is usually caused by the excessive length of connection point 12 which, in case of being bent, tend to touch each other or another circuits. The breaking of connection point 12 results from weak resistance to external forces due to weak connecting structure between connection point 12 and chip 10. For example, the error in the alignment between connection point 12 and bonding pad on the surface of printed circuit board 14 may result in a breaking of connection point 12 caused by the dragging force inherent in welding process.
Another drawback with the above flip chip package is that the difference in coefficient of thermal expansion between chip 10 and printed circuit board 14 may be big enough to bring about different expansion between them due to temperature variation in the following manufacturing process, resulting in breaking of connections.
An improvement scheme had been suggested by conventional technology in which under-fill 16 is added between chip 10 and printed circuit board 14 after they are connected. The under-fill 16 is a kind of resin such as epoxy. However, the gap between chip 10 and printed circuit board 14 is usually so narrow that it is impossible to force epoxy resin into the gap by molding transfer process. Instead, epoxy resin must be painted around the edge of chip 10, thereby penetrate, based on capillary action, into the gap between chip 10 and printed circuit board. The scheme is accompanied with enormous time consuming, and can't control or detect the extent to which the epoxy resin penetrate into the gap, and may easily produce air bubbles. Another drawback is that reworking is not feasible afterwards.
It is critically important to choose a kind of material with less viscosity, in order to enable the flowing of epoxy resin into the gap between chip 10 and printed circuit board 14. However, material with less viscosity is usually less thermally conductive, thereby can't effectively help chip 10 to dissipate heat.
Therefore solutions to the problems and difficulties left by conventional schemes for improving flip chip package are now suggested by the present invention.